System for lubricating and cooling a mechanical assembly

ABSTRACT

System for lubricating and cooling a mechanical assembly  
     According to the invention, this system comprises a main device ( 2 ) and an auxiliary backup device ( 3 ), which comprises: 
         at least one reservoir ( 10 ) of lubricating and cooling liquid independent of the main device ( 2 );    at least one source ( 11 ) of pressurized gas; and    at least one spray nozzle ( 17, 18 ) which is fed, on the one hand, with lubricating and cooling liquid at a pressure at most equal to 2 bar (2.10 −5  pascal) from said reservoir ( 10 ) and, on the other hand, with pressurized gas from said source ( 11 ), said nozzle being able to spray a mist of lubricating and cooling liquid onto said mechanical assembly ( 1 ) so as temporarily to supplement the defective main device ( 2 ).

BACKGROUND OF THE INVENTION

The present invention relates to a system for lubricating and cooling amechanical assembly. Although not exclusively, it is particularly wellsuited to lubricating and cooling a transmission gearbox, particularly amain transmission gearbox, usually used on board helicopters. Thus, thepresent invention will be described more particularly hereinafter inrelation to this application.

It is known that, for correct operation, such a transmission gearbox islubricated and cooled, generally by a device which circulates alubricating and cooling liquid, such as oil. In addition, to preventsaid transmission gearbox from being able to be damaged or evendestroyed through lack of lubrication and cooling in the event of thisdevice failing during flight, a backup device is provided whose purposeis to, at least partially, lubricate and cool said transmission gearboxto allow the helicopter to continue to fly for a predetermined survivaltime.

DESCRIPTION OF THE PRIOR ART

For example, American patent U.S. Pat. No. 4,717,000 has alreadydisclosed a system for lubricating and cooling helicopter transmissiongearboxes comprising a main device which circulates a stream of oilunder pressure through said transmission gearboxes and a backup devicewhich is set in operation automatically or manually when said maindevice becomes defective. This backup device comprises:

-   -   a reservoir connected to said main device so as to fill with        lubricating and cooling liquid from said main device;    -   a source of pressurized air, consisting of a compressor stage of        the engine of said helicopter; and    -   spray nozzles fed, on the one hand, with pressurized lubricating        and cooling liquid from said reservoir and, on the other hand,        with pressurized gas from said compressor stage, said spray        nozzles being able to spray a mist of lubricating and cooling        liquid onto certain components of said transmission gearboxes so        as temporarily to supplement the defective main device.

In that known system, the lubricating and cooling liquid is contained insaid reservoir at the relatively high pressure (at least 10 bar=10⁻⁴pascal) of the main device and, should the latter fail, is expelledtherefrom by the action of the compressed air produced by saidcompressor stage, the pressure of which has to overcome that of theliquid in the reservoir. The result of this is that the lubricating andcooling liquid sent to said nozzles is at a high pressure, itself equalto at least 10 bar (10⁻⁴ pascal). In consequence, the backup deviceconsumes a significant amount of lubricating and cooling liquid and thereservoir of the backup device needs to be of large capacity, thuscausing its mass and bulk to be high.

The object of the present invention is to overcome these disadvantagesand to make it possible to produce a lubricating and cooling systemwhich, for a backup device with the same predetermined survival time,requires only a reservoir with a capacity much lower than that of theknown system described hereinabove.

SUMMARY OF THE INVENTION

To this end, according to the invention, the system for lubricating andcooling a mechanical assembly such as a helicopter transmission gearbox,said system comprising:

-   -   a main lubricating and cooling device circulating a stream of        lubricating and cooling liquid through said mechanical assembly        at a relatively high pressure; and    -   an auxiliary backup device set in operation automatically or        manually when said main device becomes defective, said backup        device comprising:        -   at least one reservoir of lubricating and cooling liquid;        -   at least one source of pressurized gas;        -   at least one spray nozzle which is fed, on the one hand,            with pressurized lubricating and cooling liquid from said            reservoir and, on the other hand, with pressurized gas from            said source, which is able to spray onto a mist of            lubricating and cooling liquid said mechanical assembly so            as temporarily to supplement the defective main device,    -   is notable in that:        -   said reservoir of the auxiliary backup device is independent            of said main device; and        -   said spray nozzle is fed with lubricating and cooling liquid            from said reservoir at a pressure at most equal to 2 bar            (2.10⁻⁵ pascal).

What happens, according to the invention, because the reservoir of theauxiliary backup device is independent of the main device, that is tosay because it has no hydraulic communication therewith, is that thelubricating and cooling liquid sent to the spray nozzles can be at apressure far lower than that of the liquid of the main device, at mostequal to 2 bar (2.10⁻⁵ pascal) and, preferably, roughly equal to 1 bar(10⁻⁵ pascal). The result of this is that, for the same predeterminedsurvival time, the consumption of the backup device according to thepresent invention is far lower than that of the known system, whichmeans that the amount of lubricating and cooling liquid needed forbackup purposes is also far lower. As a result, the capacity, the massand the bulk of the reservoir are considerably reduced.

Such a low pressure of the lubricating and cooling liquid used forbackup purposes may be obtained in various ways. For example:

-   -   the lubricating and cooling liquid contained in said reservoir        is pressurized by said source of pressurized gas feeding said        spray nozzle, for example a compressor stage of the helicopter        engine, and a pressure and flow limiter is arranged between said        reservoir and said spray nozzle; or alternatively    -   the lubricating and cooling liquid contained in said reservoir        is pressurized by an auxiliary gas source, for example a        pressurized gas cylinder, independent of said pressurized gas        source feeding said spray nozzle, and a pressure and flow        limiter is arranged between said reservoir and said spray        nozzle; or alternatively still    -   the lubricating and cooling liquid contained in said reservoir        is pressurized by a pump the outlet of which is connected to        said reservoir by a bypass comprising a calibrated valve that        opens as soon as the outlet pressure of said pump becomes higher        than said feed pressure of the spray nozzle.

It is also noted that, because the reservoir of the auxiliary backupdevice is independent of the main device, it is easy and advantageousfor said reservoir to be arranged some distance away from saidmechanical assembly so that said lubricating and cooling liquid itcontains does not experience the effect of the heat given off by saidmechanical assembly.

Thermal degradation of the liquid contained in said reservoir is thusavoided.

When the system according to the present invention comprises a number ofspray nozzles, these may be fed with pressurized gas and withlubricating and cooling liquid through a splitter.

In addition, these nozzles may be split into groups and all the nozzlesin one group may be fed with pressurized gas and with lubricating andcooling liquid by a common feed device, all said common feed devicesthemselves being fed with pressurized gas and with lubricating andcooling liquid by said splitter.

BRIEF DESCRIPTION OF THE DRAWINGS

The figures of the appended drawing will make it easy to understand howthe invention may be achieved. In these figures, identical referencesdenote similar elements.

FIG. 1 schematically illustrates a lubricating and cooling systemaccording to the present invention.

FIGS. 2 and 3 depict, in views similar to FIG. 1, alternative forms ofembodiment of the lubricating and cooling system according to theinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 schematically depicts the main transmission gearbox 1 of ahelicopter (not depicted) and its lubricating and cooling system 2, 3.

This lubricating and cooling system comprises a main device 2circulating through said main transmission gearbox 1 a stream of mainlubricating and cooling liquid, essentially oil or some similar liquid.This main device comprises a closed-loop circuit 4 through which saidmain liquid circulates under the action of a pump 5. The circuit 4introduces said main liquid at 6 into the main transmission gearbox 1and, having lubricated and cooled the internal components of said maintransmission gearbox (these components are not depicted), this mainliquid is collected at 7 by said circuit 4. After filtering at 8, themain liquid thus collected is returned to a tank 9, from which it isonce again circulated through the circuit 4 by the pump 5. The latterimparts to said main liquid a pressure generally of the order of around10 bar.

The lubricating and cooling system additionally comprises an auxiliarybackup device 3 set in operation when said main device 2 becomesdefective, so as temporarily to maintain lubrication and cooling of theinternal components of the main transmission gearbox 1 and thus preventthe latter from becoming damaged or even destroyed.

The auxiliary backup device 3 comprises a reservoir 10 of backuplubricating and cooling liquid, completely independent of the maindevice 2, that is to say that the reservoir 10 has no hydraulicconnection with the circuit 4. The backup liquid (oil or similarproduct) contained in the reservoir 10 is pressurized by compressed airfrom a compressor stage 11 of the engine (not depicted) of thehelicopter. This compressed air is sent to the reservoir 10 through afilter 12, a control valve 13 which is normally closed, for example ofthe electrically operated valve type, a cooler 14 and a connection 10Abetween the outlet of the latter and said reservoir 10. The cooler 14may be of the heat exchanger type.

In addition, the reservoir 10 is preferably arranged some distance awayfrom the main transmission gearbox 1 so that the backup lubricating andcooling liquid it contains does not experience the effect of the heatgiven off by said main transmission gearbox.

Furthermore, the auxiliary backup device 3 comprises groups 15, 16 ofspray nozzles 17, 18, for example mounted on the housing 19 of the maintransmission gearbox 1. The spray nozzles 17, 18 of the groups 15, 16are of a known type which, fed with pressurized gas and with liquid thatis to be sprayed, are able to spray said liquid in the form of a mist.In consequence, each spray nozzle 17 of the group 15 is connected, by adouble connection (pressurized gas/liquid for spraying), to a feeddevice 20 able to deliver pressurized gas and liquid for spraying.Likewise, each spray nozzle 18 of the group 16 is connected, by a doubleconnection (pressurized gas/liquid for spraying), to a feed device 21able to deliver pressurized gas and liquid for spraying. In addition,the feed devices 20, 21 may themselves be fed with pressurized gas andwith liquid for spraying from a splitter 22.

This splitter 22 may receive compressed air from the compressor stage11, by virtue of a connection with the outlet of the cooler 14, via anonreturn valve 23 and a filter 24. Likewise, the splitter 22 mayreceive backup lubricating and cooling liquid by virtue of a connectionwith the reservoir 10, via a pressure and flow limiter 25, a nonreturnvalve 26 and a filter 27. Such a pressure and flow limiter 25 mayconsist of a calibrated pressure relief valve.

The control valve 13 may be opened manually using a member 28, forexample available to the helicopter pilot, or via a pressure sensor 29arranged in the circuit 4.

Thus, when the main circuit 2 becomes defective, for example following abreakdown of the pump 5 or a leak from the circuit 4, the pressure ofthe main lubricating and cooling liquid in said circuit 4 decreases veryrapidly. The drop in pressure is detected by the sensor 29, which eitheris connected to an alarm (not depicted) alerting the pilot who can thenact on the member 28, or directly opens the valve 13. Whatever the modeof operation (manual using the member 28 or automatic via the sensor29), the valve 13 allows fluid through, which means that the compressedair from the compressor stage 11 is sent to the cooler 14, possiblyafter filtering at 12. The cooler 14 therefore feeds compressed air toboth the splitter 22 (through the nonreturn valve 23 and the filter 24)and the reservoir 10 containing the backup lubricating and coolingliquid (via the connection 10A). The latter liquid is therefore alsosent under pressure to the splitter 22, through the pressure and flowlimiter 25, the nonreturn valve 26 and the filter 27. By virtue of thelimiter 25, which may be of any known type, the pressure of the backuplubricating and cooling liquid at the splitter 22 is at most equal to 2bar (2.10⁻⁵ pascal) and preferably equal to 1 bar (10⁻⁵ pascal).

The splitter 22 therefore feeds the feed devices 20 and 21 and thenozzles 17 and 18 with backup liquid (at this low pressure) and withcompressed gas. These nozzles 17 and 18 are therefore able to spray amist of said backup liquid onto the internal components (or some ofthem) of the gearbox 1, to lubricate and cool them so as to allow thegearbox (and therefore the helicopter) to survive in spite of thefailure of the main device 2.

It will be noted that, because the pressure with which the backuplubricating and cooling liquid is sent to the nozzles 17 and 18 is low,the consumption of these nozzles is also low, which means that, for apredetermined survival time, the amount of backup liquid needed, andtherefore also the volume of the reservoir 10, can be small. Thus theapplicant company has been able to discover that, on one of itshelicopters, the amount of backup lubricating and cooling liquid could,for the same survival time, be reduced from 35 liters to 10 liters byimplementing the present invention.

In the alternative form of embodiment depicted in FIG. 2, there can befound all the elements 1 to 29 described hereinabove, arranged in thesame way except as regards the connection 10A between the cooler 14 andthe reservoir 10, which connection has been omitted.

By contrast, the system of FIG. 2 has, in addition by comparison withthat of FIG. 1, a capsule 13 of pressurized gas and another valve 31,normally closed and in parallel with the valve 13. This valve 31 mayalso be of the electrically operated valve type. It can be opened by themember 28 and/or the pressure sensor 29, in the same way as wasdescribed hereinabove in respect of the valve 13, the valves 13 and 31being operated jointly and simultaneously.

In the light of the foregoing explanations, it will therefore be readilyunderstood that, in the event of the main device 2 becoming defective,the valves 13 and 31 are opened together so that the splitter 22, andtherefore the spray nozzles 17 and 18, are fed with compressed air, asabove, through the valve 13, the cooler 14, the nonreturn valve 23 andthe filter 24, and with backup lubricating and cooling liquid by theaction of the compressed gas capsule 30, through the pressure and flowlimiter 25, the nonreturn valve 26 and the filter 27. As before, thepressure of the backup liquid at the nozzles 17 and 18 is at most equalto 2 bar (2.10⁻⁵ pascal) and preferably equal to 1 bar (10⁻⁵ pascal).

In the other alternative form of embodiment depicted in FIG. 3, therecan again be found all the elements 1 to 24 and 26 to 29 describedhereinabove with reference to FIG. 1 and arranged in the same way, theconnection 10A between the cooler 14 and the reservoir 10 however beingomitted. In addition, the pressure and flow limiter 25 is also omitted.The connection 10A and the limiter 25 are replaced by a device 32comprising, on the one hand, a pump 33 which can be operated in parallelwith the valve 13 by the member 28 and/or the sensor 29 and, on theother hand, a bypass comprising a nonreturn valve 34, which is mountedin parallel with the pump 33, between the outlet thereof and thereservoir 10. The opening of the nonreturn valve 34 is set to be justhigher than the pressure desired for the nozzles 17 and 18. The pump 33is, for example, of the positive-displacement type and performsregulation. It may be of variable output and adjustable pressure type.

Thus, when the main device 2 becomes defective, the member 28 and/or thepressure sensor 29 simultaneously open the valve 13 (as was the case forthe systems in FIGS. 1 and 2) and actuate the pump 33 which sends thebackup liquid contained in the reservoir 10 to the splitter 20 and tothe nozzles 17 and 18. If the pressure of this backup liquid exceeds thedesired low value (at most equal to 2 bar), then the nonreturn valve 34opens and the liquid is returned to the reservoir 10. The nonreturnvalve 34 therefore acts as a pressure limiter.

1-10. (Canceled).
 11. A system for lubricating and cooling a mechanicalassembly such as a helicopter transmission gearbox, said systemcomprising: a main lubricating and cooling device circulating a streamof lubricating and cooling liquid through said mechanical assembly at arelatively high pressure; and an auxiliary backup device set inoperation automatically or manually when said main device becomesdefective, said backup device comprising: at least one reservoir oflubricating and cooling liquid; at least one source of pressurized gas;at least one spray nozzle which is fed, on the one hand, with thelubricating and cooling liquid from said reservoir provided underpressure and, on the other hand, with the pressurized gas from saidsource, and which is able to spray a mist of the lubricating and coolingliquid onto said mechanical assembly so as temporarily to supplement thedefective main device, wherein: said reservoir of the auxiliary backupdevice is independent of said main device; and a pressure and flowlimiter is arranged between said reservoir and said spray nozzle; saidspray nozzle is fed with the lubricating and cooling liquid from saidreservoir at a pressure at most equal to 2 bar (2·10⁵ pascal).
 12. Thesystem as claimed in claim 11, wherein said spray nozzle is fed with thelubricating and cooling liquid at a pressure roughly equal to 1 bar (10⁵pascal).
 13. The system as claimed in claim 11, wherein said independentreservoir of the lubricating and cooling liquid is arranged somedistance away from said mechanical assembly so that said lubricating andcooling liquid it contains does not experience the effect of the heatgiven off by said mechanical assembly.
 14. The system as claimed inclaim 11, wherein the lubricating and cooling liquid contained in saidreservoir is pressured by said source of pressurized gas feeding saidspray nozzle.
 15. The system as claimed in claim 11, wherein thelubricating and cooling liquid contained in said reservoir is pressuredby an auxiliary gas source independent of said pressurized gas sourcefeeding spray nozzle.
 16. The system as claimed in claim 11, in whichsaid mechanical assembly is driven by an engine provided with at leastone compressor stage, wherein said source of pressurized gas feedingsaid spray nozzle is formed by said compressor stage.
 17. The system asclaimed in claim 15, wherein said auxiliary gas source, independent ofsaid pressurized gas source feeding spray nozzle, comprises apressurized gas container.
 18. The system as claimed in claim 11,comprising a number of spray nozzles, wherein said nozzles are fed withthe pressurized gas and with the lubricating and cooling liquid througha splitter.
 19. The system as claimed in claim 18, wherein said nozzlesare split into groups and all the nozzles in one group are fed with thepressurized gas and with the lubricating and cooling liquid by a commonfeed device, all said common feed devices themselves being fed with thepressurized gas and the lubricating and cooling liquid by said splitter.